Spark plug



Sept. 4, 1934. E. w. MiTcHEl.

SPARK PLUG Filed May 23, 1932 if ...llllllllllls INVENTOR Patented Sept. 4, 1934 UidiTED STATES PATENT @FFlCE Z Claims.`

This invention relates to spark plugs for internal combustion engine use, and has for its object an improved organization of parts whereby all parts liable to impairment under long use are rendered quickly cheaply replaceable, and the wasteage of certain expensively machined parts inci- Lent to the discarding of poorly firing plugs is largely avoided. Another cause which contributes heavily to the ineiiiciency and early discarding of many oi the present forms of spark plugs centers about the fact that the anode and cathode terminals between which the spark cours are mounted upon individually separate and removable parts of the spark plug assembly, l5 as for example one on the metallic outer shell and the other upon the porcelain center. The comparatively slight variances in the spacing between these terminals, due to variances in the iit of the component parts in different spark plug units as assembled, even though of only a minute fraction of an inch difference, often make for either the successful functioning of the spark plug assembly or its failure as a spark-furnishing medium. As will be hereinafter pointed out, in my construction, on the other hand, the inbody, preferably oi porcelain or some wellknown equivalent material, carries both sparkproducing terminals whose careful adjustment and spacing can be cared for incident to its manufacture, thus avoiding condemning variances in the distance between the terminals incident to the supported presence of one terminal upon the outer shell.

A further and important advantage oifered by my improved construction arises from the wellknown fact that a large percentage of the breakage of the porcelain part of the spark plugs now generally used is caused by a nut-imposed strain thereon, due to an effort to make 'the spark plug cl0 as installed as nearly gas-tight as possible. When the porcelain ci a spark is thus broken, its usefulness is of course gone, and even when, under ordinary service conditions, a spark-plug becomes so fouled that its points can no longer give off the needed ignition spark, it is now thrown away in its entirety, including the still perfectly good nuts, binding posts and other metal parts. This causes an effort on the part of every user to make a spark plug last as long as possible, and 00 of course a wastage of gasoline and its derivative, the explosive mixture, results in the later stages of its use before being finally discarded.

In the improved construction of spark plug here offered a clear structural distinction is made 25 between the really permanent and relatively un- (Cl. 12B- 169) injurable metal parts, such as the nuts and threaded neck piece, and the spark-producing parts, by forming the latter, including the p0rcelain insulating body, as a sort of cartridge or removable element which can easily be .sub- 00 stituted for a similar one which has outlived its usefulness. Moreover, in forming this part I structurally integrate, with and about the porcelain, a metal shell, which serves to carry one of the spark points on its lower edge and adjacent 05 companion point which extends through the c .er of the porcelain, and which sleeve is as well the recipient, on two of its opposed shoulders or taper. of all of the nut-tightening strain which cannot be breakingly transmitted to the porcelain. Thus a minimum of breakage of po la n sleeves results, and the very cheapness the subs 'tutable part, as compared with the present cost of an entire spark plug structure, amounts to an incentive to keep in use and clean only such replaceable fillers as are still new enough to operate with a maximum of eniciency. Such a construction also makes it easy to install various types or sizes of rells in the same metal shell and nut-integrated structure according to the variant ignition requirements of different motors.

My prefer ed form of construction embodying the improvements hereinabove outlined is illustrated in the accompanying drawing whereinz- Figure 1 is an elevational view of a completely1 assembled spark plug.

Figure 2 is a largely sectional elevational view of the spark plug shown in Figure l.

Figure 3 is br Azen away perspective of the 90 saine plug designed to bring out even more clearly the inter-re tion of thD parts.

Figure is a partly broken away and sectional elevational view of a evable ii er or partly porcelain cartridge disassociated from the eXternal holding shell.

Figure .5 is a lower el vational view of the spark plug as illustrated 'n l and 2, being taken along the line 5-5 of the latter and looking in the direction of the arrows there shown.

6 a sectional view of the device taken along the horizontal line 6-5 of Figure 2 and ,looking the direction oi the arrows there view of a fully assembled spark plug of slightly modified form in that provision is made for an annular gas swirling chamber well up toward the middle of the plug as assembled.

A repr'esents the usual threaded shell, which is designed to be screwed into a correspondingly threaded aperture in the cylinder wall of an internal combustion engine, and B represents the knurled or milled top portion thereof designed to be engaged by the ngers or by pliers when screwing the sp plug in place. As brought out in sectional Figures 2 3 particularly, the upinterior face of the shell or collar A is screwthreaded for the engagement therein of the correspondingly threaded annular nut C.

It will ce noted that the interior bore of the shell n. is diminished about half down its length as a whole in order to provide a shoulder D, of substan y the saine breadth as the thickness of the wa diametri t is just such to of the ll of the annular nut C and that the cel si e of the lower portion of the bore permit a slip fit therewithin collar or sleeve E, illustrated by itself rn .re 7. The upper portion of this sleeve i of larger diameter, beginning at the peA zo as to constitute a shoulder of ccmplern itary size function to that located at the poi- M in th, outer shell, and that the top edge ci this enlarged portion of the collar E preferably, the i not necessarily, bevelled, as

for the against it after instalion within the shell A of the complementarily at bevelled low edge of the annular nut C. The porcelain body I-l, being held in position within the collar E, particularlyv by the inbent 'top edge thereof, extends nearly to the level of the bottom edge of said collar TJ; through its center extends the stem J, the lower end of which projects sufficiently beyond the lower end of the porcelain body El to constitute one of the sparkpplyi--g elements, the inbent terminal G, which is carried by the lower edge of the shell E constituting the other or" such terminals. The upper end of this stein being threaded, as at J for the -engagement thereabout cf the cap nut K. As

brought out particularly in Figures 2, 3, and 4, lower end of the porcelain body is tapered sufficiently so as tc form an air space L between its surlace and the interior surface of the sleeve or shell E.

ln the slightly modified form illustrated in iigure 8 the structural features hereinabove outlined rnuch the same, except for the fact that, at a position corresponding to the shoulder D in the earlier forms, a double shoulder, as M and N, is formed in the interior of the shell A, thus lea'f* g in addition to the tapering annular space 1. very noticeable annular chamber Q into unich the gases swept past the sparking points G J proceed and be swirled about in a way has been found to conduce materially to the draught effected cleansing of the spark plug points in the manner already mentioned as to the form shown in Figures 2, 3, and 4. 'Ihe shoulder M in this form serves as the abutment against which the extreme outer periphery of the shoulder F on the sleeve rests, while the shoulder N marks the ...ne of demarcation between the enlarging space which forms the cham er N and the taperl made it possible to easily and cheaply substitute worn or fouled spark terminals merely by the removal of the relatively inexpensive filler or cartridge constituted by the shell E and the porcelain structure H, without disturbing the relatively expensive machined shell and nut parts which now represent a total loss when substitution of new spark plugs for old ones is indulged in, and which for an indenite time, in-

deed as long as the engine structure lasts, can

continue to be of unimpaired efficiency.

The greatest virtue of this removable ller structure, however, lies in the fact that in its initial installation, as Well as at al1 times thereafter, no strain is put upon the procelain structure regardless of how tightly the annular threaded nut C may be screwed down within the body A in the effort to make the plug gas tight, since all of the compressive strain is imposed upon the bevelled top edge and the shouldered or tapered portion F of the metal shell; and this strain being truly longitudinal of the filler as a whole falls upon the flared top edge of the metal shell without being transmitted to the easily fractured porcelain body. However, when removal thereof and substitution of a new filler is desired the old one may be lifted out as soon as the annular nut C has been unscrewed.

What I claim is:

1. In a spark plug construction, an outer supporting bushing having an enlarged and internally threaded upper portion and a smaller downwardly projecting tubular portion, an internal shoulder between said portions of the bushing,

a tubular shell having a lower portion freely extending through the smaller tubular portion of the bushing and an enlarged upper portion seated at its lower extremity against said shoulder, an insulating electrode retainer body extending through the shell and projecting from the top thereof and from the supporting bushinfr and having an enlarged central portion retained within said enlarged upper portion cf the shell, said upper portion of the shell being inturned over the top of said enlarged portion of the jy wardly projecting tubular portion, an internal shoulder between said enlarged and tubular portions of the bushing, a generally tubular shell having a lower portion freely extending through the tubular portion of the bushing and an enlarged upper portion seated at its lower extremity against said shoulder, an insulating electrode retainer body extending through the shell and projecting from the top thereof and from the supporting bushing and having an enlarged central portion retained within said enlarged upper portion of the shell, said upper portion of the shell being inturned over the top of the enlarged portion of the retainer body, an electrode extending through the retainer body, and a jam nut encircling the upper portion of the retainer body and bearing against the inturned top portion of the shell, the internal diameter of the jam nut being substantially the same as the internal diameter of the enlarged upper portion of the shell.

EDWARD W. MI'ICl-IEL.

lOG 

